Criminals in Italy are increasingly making phone calls over the internet in order to avoid getting caught through mobile phone intercepts, police say.
Officers in Milan say organised crime, arms and drugs traffickers, and prostitution rings are turning to Skype in order to frustrate investigators.
The police say Skype's encryption system is a secret which the company refuses to share with the authorities.
Investigators have become increasingly reliant on wiretaps in recent years.
Customs and tax police in Milan have highlighted the Skype issue.
They overheard a suspected cocaine trafficker telling an accomplice to switch to Skype in order to get details of a 2kg (4.4lb) drug consignment.